Polyamide resins each involving a diamine and a dicarboxylic acid as the starting materials are widely used in various fields. The method for producing such a polyamide resin is generally as follows. Specifically, first, a nylon salt (polyamide salt) is prepared by using a diamine and a dicarboxylic acid, and the nylon salt is polymerized under pressure.
In the photosensitive resin structure used in relief printing, generally a photosensitive resin layer is laminated on a polyester film as a support. The method for obtaining a printing plate by making a photosensitive resin printing plate by using the photosensitive resin structure is as follows. Specifically, first, ultraviolet exposure (back exposure) is performed on the entire surface of the photosensitive resin layer through the polyester film to form a thin uniform cured layer. Next, a negative film is disposed on the photosensitive resin layer, image exposure (relief exposure) is performed on the photosensitive resin layer through the negative film, and thus the photosensitive resin layer is photocured according to the pattern of the negative film. Subsequently, the unexposed area (namely, uncured area) of the photosensitive resin layer is cleaned with a developing liquid to form an intended image, namely, a relief image, and thus a printing plate using a polyester film can be obtained. Recently, it has become possible to obtain a printing plate by performing direct exposure, without through the intermediary of a negative film, with a device such as a laser, or by applying, for example, a method in which exposure is performed after the removal of a black mask with a laser.
In the printing plate using a polyester film, obtained as described above, the photosensitive resin layer is usually as extremely thick as 1 mm or more and large in the cure shrinkage at the time of exposure, and hence there is an apprehension that the adhesiveness of the interface between the photosensitive resin and the polyester film is degraded. Usually, a printing plate is used under the condition that the polyester film surface is fixed, with a member such as a double-sided tape, to the plate cylinder of a printing press. However, in the case where a printing plate is used for printing, when the printing plate is made to pass between the plate cylinder and the impression cylinder of the printing press, shear stress is exerted to the printing plate so as to peel the photosensitive resin layer from the polyester film, and hence the printing is required to be ceased in some cases. When the printing plate is detached from the plate cylinder at the time of completion of the printing, the photosensitive resin layer and the polyester film are peeled from each other, and hence the printing plate is broken and cannot be reused in some cases.
In view of such current circumstances as described above, a printing plate in which a photosensitive resin layer and a polyester film are made to strongly adhere to each other so as not to be easily peeled from each other is demanded. However, the photosensitive resin layer and the polyester film are significantly different from each other in properties such as polarity, and hence it is difficult to make the photosensitive resin layer and the polyester film strongly adhere to each other.
In a laminate in which a photosensitive resin layer and a polyester film are laminated on each other through the intermediary of an adhesive layer, the composition of the photosensitive resin layer affects the adhesiveness of the adhesive layer in some cases. For example, the migration of the photopolymerization initiator and the ethylenically unsaturated compound included in the photosensitive resin layer into the adhesive layer causes the polymerization reaction in the adhesive layer at the time of exposure and hence the cure shrinkage of the adhesive layer is caused in some cases. Consequently, interfacial peeling occurs in some cases between the polyester film and the adhesive layer, or between the photosensitive resin layer and the adhesive layer.
Accordingly, for the purpose of developing sufficient adhesive force between the polyester film and the photosensitive resin layer, it is necessary to investigate the composition of the photosensitive resin layer. However, the photopolymerization initiator and the ethylenically unsaturated compound are essential components for imparting the photosensitivity. Accordingly, it is difficult to obtain a photosensitive resin layer having a strong adhesive force with the polyester film without impairing the intrinsic nature of the photosensitive resin layer.
Thus, a large number of investigations have been made on the adhesive for making the photosensitive resin layer and the polyester film adhere to each other. For example, an adhesive made of a reaction product between a mixture including a polyol having a polyester structure, a polyurethane structure, or both of these structures and a hydroxyl group-containing ethylenically unsaturated compound and a multifunctional isocyanate has been investigated (JP2001-264959A). However, in the case of JP2001-264959A, the adhesive force is not sufficient, and hence it is necessary to separately form a primer layer or an adhesive layer. Consequently, disadvantageously the steps become complicated or an increase in costs is caused.
An adhesive including an ethylene-vinyl acetate copolymer having a vinyl acetate content of 11 to 50% by mass has also been investigated (JP2004-109443A). However, in the case of JP2004-109443A, the thickness of the adhesive layer is extremely large, and adhesiveness is developed at normal temperature to an extent more than necessary in some cases. Accordingly, a release film for the prevention of adhesion is needed until the photosensitive layer is put into use, and hence disadvantageously the steps become complicated or an increase in costs is caused.
Another adhesive including an acrylic resin and/or an aromatic polyurethane resin has also been investigated (JP4067849B). Yet another adhesive including a reaction product between a polyol having a polyester structure, a polyurethane structure, or both of these structures and a hydroxyl group-containing ethylenically unsaturated compound has also been investigated (JP2000-155410A).
However, in the cases of the adhesives of JP4067849B and JP2000-155410A, it is difficult to satisfactorily adhere to all the photosensitive resins having various compositions, and it is essential to modify the composition of the photosensitive resin according to the adhesive. In other words, it is essential to use, in the photosensitive resin, various base polymers, various ethylenically unsaturated compounds, various photopolymerization initiators or plasticizers, for the purpose of imparting the hardness, flexibility and resolution optimal as the printing plate. However, if such substances are used, the affinity or the compatibility between the photosensitive resin and the adhesive layer is altered, and hence there is a possibility that the performances as the printing plate are impaired.